The present invention relates to a liquid crystal composition and to a liquid crystal device and liquid crystal display apparatus using the liquid crystal composition. More specifically, the present invention relates to a liquid crystal composition comprising a liquid crystal and a gel-forming compound which forms a gel with the liquid crystal and having a discotic liquid crystal phase and assuming a supermolecular structure, as well as to a liquid crystal device and liquid crystal display apparatus using the liquid crystal composition.
With the development of information equipment, societal need for a low power consumption-type thin display device has considerably increased in recent years. In order to meet such a need, a liquid crystal display device as a device with a smaller thickness and a lower power consumption has been extensively developed. Particularly, liquid crystal display devices using a nematic liquid crystal or a ferroelectric liquid crystal have already been commercialized.
Such a liquid crystal composition, however, generally requires many constituent compounds in a mixture in order to enlarge the mesomorphic temperature range and driving (voltage-transmittance) and optical characteristics, thus necessitating accumulated experiences or experiments and a complicated mixing step of many constituent compounds possessing different physical and mesomorphic properties. Further, when a color display is performed, a liquid crystal device using the liquid crystal composition is required to employ an additional member, such as a color filter, thus resulting in a complicated device structure.
In recent years, many liquid crystal compositions comprised of a relatively smaller number of components have been proposed.
Specifically, a liquid crystal composition comprising a low molecular weight liquid crystal and a low molecular weight amorphous compound and having a structure such that the low molecular weight amorphous compound forms a domain of a network structure via hydrogen bonds and the low molecular weight liquid crystal is dispersed in the domain has been proposed (Japanese Laid-Open Patent Application (JP-A) 8-254688). Liquid crystal compositions comprising a liquid crystal and a low molecular weight compound by which the liquid crystal is gelatinized have been proposed (JP-A 11-52341, JP-A 11-21556 and JP-A 11-256164). Further, a liquid crystal composition comprising a mixture of a rod-shaped liquid crystal with a dendrimer or a discotic liquid crystal has been disclosed (JP-A 9-234984).
With respect to a color liquid crystal device without a color filter, many studies thereon have been made since a report as to a cholesteric liquid crystal device by Martin Sohadt et al., xe2x80x9cLiquid-Crystal Device and Materialsxe2x80x9d, vol. 1455, pp. 214-224 (1991) and include, e.g., one regarding a liquid crystal composition comprising a nematic liquid crystal and a chiral dopant (agent) added thereto. According to these liquid crystal devices, it is possible to effect selective reflection based on a helical structure of aligned liquid crystal molecules, thus allowing color display. The color display has also been realized by using holography (e.g., JP-A 11-2802).
However, these documents have encountered the following difficulties.
JP-A 8-254688 requires an amount of at least 10 wt. % of the low molecular weight amorphous compound for forming the network structure. According to JP-A 11-52341, JP-A 11-21556 and JP-A 11-256164, it has been reported that it is possible to effect alignment control of liquid crystal molecules by utilizing hydrogen bonds formed between self-assembly (association) type molecules, but actual molecular structures have not been confirmed. Further, JP-A 9-243984 has reported that it is possible to effect a low voltage drive, but it is silent about an improvement in contrast.
The above-mentioned color liquid crystal devices using the cholesteric liquid crystal, the nematic liquid crystal doped with the chiral dopant and holography generally require a three-layer structure comprising, e.g., cholesteric liquid crystal layers of red (R), green (G) and blue (B) disposed in succession to effect multi-color display based on material control manner, thus failing to provide multi-color display states based on an electrical drive scheme. As a result, such color liquid crystal devices have a complicated cell structure and fail to attain optical advantages.
In view of the above problems, a principal object of the present invention is to provide a liquid crystal composition, device and display apparatus having solved the above problems.
A specific object of the present invention is to provide a liquid crystal composition lowered in flowability of liquid crystal molecules originally showing fluidity by using a discotic gel-forming compound capable of forming a supermolecular structure.
Another object of the present invention is to provide a liquid crystal device and liquid crystal display apparatus using the liquid crystal composition capable of increasing a contrast and controlling color display states based on selective reflection or transmittance of light by electrical control of voltage, frequency, etc.
According to the present invention, there is provided a liquid crystal composition comprising: at least a liquid crystal and a gel-forming compound forming a gel with the liquid crystal, wherein the gel-forming compound has a discotic liquid crystal phase.
According to the present invention, there is also provided a liquid crystal device comprising: a pair of electrodes and a liquid crystal composition disposed between the electrodes, wherein the liquid crystal composition comprises at least a liquid crystal and a gel-forming compound forming a gel with the liquid crystal, said gel-forming compound having a discotic liquid crystal phase.
According to the present invention, there is further provided a liquid crystal display apparatus using the liquid crystal device.